By Allison Adato
Updated July 09, 2007 12:00 PM

Here’s the deal: If you’re taking the new over-the-counter diet drug Alli, and you want the chicken with crispy noodles, you have to really, really want the chicken with crispy noodles.

Against her better judgment, Alli-user Caryn Eyring, 39, ordered just such a chicken appetizer during a recent dinner out. “I knew darn well it was cooked in oil,” says Eyring, a Glendale, N.Y., secretary. But she ate it anyway, and the next day suffered what she—and the official Alli Web site—calls “a treatment effect,” or an “oily diarrhea” that occurs when a person eats more than 15 grams of fat in a single meal.

Therein lies one of the biggest hurdles that Alli, the first FDA-approved over-the-counter diet drug, faces in the marketplace. In February the FDA green-lit Alli for sale at half the dosage of its Rx counterpart, Xenical (generic name of both: Orlistat). Because it works by blocking one-quarter of fat consumed (users are advised to take multivitamins at bedtime to replace the loss of fat-soluble vitamins A, E and D), some early adopters have underestimated the extent of the “treatment effects.” (Alli’s Web site warns, “it’s probably a smart idea to wear dark pants.”) On the message board of the site, one user writes, “Now I [know] how toddlers feel when they are trying to be potty-trained and not have an accident.” Another dubbed such incidents “alli-oops.”

Those aren’t the only concerns. Critics of Alli worry that the drug—intended for overweight adults 18 and over (see box)—will fall into the wrong hands without a doctor’s prescription. “People who are marginal may be using it,” says Dr. Lawrence Cheskin, director of Johns Hopkins Weight Management Center. “They might lose a couple of pounds; they might not.”

Others contend that the drug’s benefits—Alli’s maker GlaxoSmithKline claims 50 percent more weight loss than with a low-calorie diet and exercise alone—aren’t worth potential risks. Dr. Sidney Wolfe, of Ralph Nader’s watchdog association Public Citizen, petitioned the FDA to deny Alli’s approval, citing a study linking Orlistat to “precancerous colon lesions” in rats. Says Wolfe: “This is the height of recklessness.”

In its response the FDA wrote, “evidence … does not support a causal relationship between Orlistat and colorectal carcinoma.”

Since going on sale June 15, Alli ($50 for a two-month supply) is, anecdotally, an early hit. “Sales during the first days were ahead of expectations,” says Steve Burton, a VP at Alli maker GSK. Confirms a Pacific Palisades, Calif., pharmacist: “We’ve had it a week and can’t keep it on the shelf, it’s so popular.”

Eyring, who started at 167 lbs. and aims to be 135, says that since April (when she joined a drug trial in which Alli was provided to her free), “I’m down 21 lbs.” In part because the threat of episodes (like the post-chicken-and-crispy-noodle one) “is forcing me to cook healthier.”

Cherie Dager of Northridge, Calif., on the other hand, tried Alli and has already given it up. Before she understood how to eat with the pill, she popped one along with a bag of potato chips. “I had the most incredible pain. I literally dropped to my knees,” says Dager, 39. Her side effects “were disgusting. And I didn’t lose any weight.” Others such as Paula Miguel, 35, who was also part of the Alli trials, are sticking with it. The Sussex, N.J., accountant has lost 23 lbs. in three months with the pills, low-fat foods and walking daily. “But,” she says, “if I stopped taking Alli today, I would still keep those new habits.”